Here we have the Lord giving instructions on how to do difficult missionary work. He approves of their mission, and tells them to go to preach and establish his word. As he does so, he tells the company what they will need to do to be successful. The advice is appropriate for a modern audience as well.
[patient in long-suffering and afflictions] Very few missions are immediately successful, and missions in their early stages are even less obviously productive. Patience allows us to realize that the lack of immediate success is not evidence of lack of success. People require time. Missionaries need the time to find the right people among all of the possible converts. The potential converts need time to accept the change in their lives that will come through the acceptance of the gospel. Patience allows the missionary to wait for these natural processes to take place. This is patience in long-suffering. This is not meant to emphasize "suffering" but the other meaning of "suffer" which is to allow. To be "long-suffering" is to have the patience to allow events to develop at their own pace.
Patient in afflictions is self-directed, where the patience in long-suffering is directed to another person. Missionary tasks are not always easy, and they may lead to different types of afflictions. In the days of the Sons of Mosiah, those afflictions would have been more numerous, and potentially life-threatening. Nevertheless, they were to have patience even through those trials.
[show forth good examples unto them in me] One of the greatest tools of the missionary is their own soul. The change effected in the person of the missionary is the example before the investigator of the possibilities offered in the gospel. Anyone who would make a great change to leave a life behind and follow the Lord needs to know that the process is both possible and worthwhile. The example of the missionary is a paramount tool to show both of these aspects.
[I will make an instrument of thee in my hands] Lest any missionary forget, it is not the missionary that does the converting. The excellent missionary is an instrument, not the hand that moves the instrument. It is the Spirit that converts, through the tool of the missionary, who through faith and effort, is in the right place at the right time.